[Atomic-S (OP)]

In which medium will sound of a given wavelength travel farther before losing half its energy: a gas at low pressure, or the same gas at the same temperature but a higher pressure?

[MOD EDIT- please phrase subjects as questions in line with AUP]

[evan_au]

The attenuation of sound is lower when the gas is at a higher pressure.

This can be seen in Stokes' Law: when the density ρ is lower, the attenuation α is higher.

When the gas pressure is so low that the distance between molecular collisions is roughly the wavelength of the sound, attenuation gets very high.

[yor_on]

Or, where does sound travel faster, in air or in the sea?

http://www.waterencyclopedia.com/Re-St/Sound-Transmission-in-the-Ocean.html

[Atomic-S (OP)]

Sound travels faster in water than in air.